79% of Treatment-Experienced Patients on MK-0518 Plus OBT Achieve Viral Load of Less Than 400 Copies at Week 16

2007 has the potential to enter history books as the only year in which agents from two new HIV drug classes could receive U.S. Food and Drug Administration (FDA) approval for use in the treatment of HIV infection in the HIV treatment-experienced population. This is particularly important and clinically useful since we have learned in the past few years that, when building a new antiretroviral regimen, the use of at least two new potent agents is one of the best predictors for virologic response in a heavily treatment-experienced patient.

At the 14th Conference on Retroviruses and Opportunistic Infections, in a special late breaker session, new data on the ongoing registrational studies for new compounds were released for the first time to the public. On the program first were the results of the MOTIVATE 1 and 2 studies delivered by Pfizer, Inc., representatives, which explored the use of maraviroc (UK-427,857), a CCR5 entry inhibitor, in experienced HIV-infected patients with CXCR5-tropic virus.1,2 In these studies, we observed in general HIV RNA drops of almost 1 log with the addition of maraviroc to an optimized background therapy (OBT).

We were then presented with the data from the BENCHMRK 1 and 2 studies, by David Cooper3 (from the University of New South Wales, Sydney) and by Roy Steigbigel4 (from the State University of New York at Stony Brook), respectively. These studies evaluated MK-0518, which was recently given the generic name raltegravir (RTG) and is expected to be given the brand name Isentress, for use in the treatment of a heavily experienced HIV-infected population with virologic failure.

BENCHMRK 1 and 2 are identical, ongoing phase 3 studies that are being conducted in different countries. They are randomized, double-blind, placebo-controlled trials in which raltegravir 400 mg twice daily is compared to placebo, both in combination with an OBT selected by the investigator based on baseline resistance tests.

All patients were failing an antiretroviral regimen at the time of enrollment, with documented genotypic or phenotypic resistance to one or more drugs in each of three classes: nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs) and protease inhibitors (PIs). The results presented at this conference were based on an interim 24-week analysis, in which all patients completed at least week 16.

Both BENCHMRK studies were equal in design, enrolled a similar number of patients, had similar demographics and baseline patient characteristics, and yielded similar study results. Between both studies, 699 patients were randomized 2:1 (raltegravir:placebo) with only 22 patients total discontinuing the study at the time of this analysis (15 who were receiving raltegravir and seven on placebo). The median CD4+ cell count at baseline was approximately 154 cells/mm3 and approximately a quarter of the patients had a genotypic susceptibility score (GSS) of zero. The use of TMC114 (darunavir, Prezista) or enfuvirtide (T-20, Fuzeon) in the OBT was always counted as an active drug.

The proportion of patients achieving an undetectable viral load of less than 400 copies/mL was highly statistically significant favoring the raltegravir arm over the placebo arm. The mean change in CD4+ cell count from baseline for the pooled data at week 24 was also highly statistically significant favoring the raltegravir arm, 124 cells/mm3 versus 68 cells/mm3. For this analysis, all patients had completed at least week 16, and the results for week 24 are for just a fraction of the population that reached week 24 at the time of this analysis.

The use of raltegravir + OBT was associated with a response rate of 79% in patients with an HIV RNA of less than 400 copies/mL at week 16. The use of TMC114 + enfuvirtide as part of the OBT with raltegravir was associated with a 98% response rate, and the use of one of these two drugs with raltegravir was associated with a 90% response rate. This again reinforces the importance of selecting two or more active agents when building a new antiretroviral regimen for a heavily treatment-experienced patient.

Virologic failure was observed in 76 (16%) patients who were in the raltegravir arm versus 121 (51%) patients in the placebo arm. A partial analysis based on genotyping 41 samples of raltegravir failures showed 32 patients with changes on the integrase genotypic sequence versus nine patients with no consistent genotypic changes from baseline. In general, raltegravir failure was associated with one or two genetic resistance pathways, with other associated mutations here shown in parenthesis: N155H (with E92Q, V151I, T97A, G163R and L74M) or Q148K/R/H (with G140S/A, E138K). These mutations were proximal to the catalytic center and they are similar to the ones that have been observed in vitro.

The safety data presented in this study was equally impressive. A similar incidence of clinical adverse events was seen in the raltegravir and placebo arms. Injection site reactions were the most common adverse event, but were most likely caused by the use of enfuvirtide. The most frequent adverse event that could have potentially been caused by raltegravir was diarrhea, and this was seen with equal frequency among both study arms. Similarly, laboratory abnormalities were also divided equally among both study arms. No statisically significant dyslipidemia, or elevation in creatinine or liver function tests were identified with the use of raltegravir over placebo.

In this interim preliminary data, the use of raltegravir + OBT, in patients with advanced HIV infection who had been failing previous antiretroviral drugs and who had evidence of multidrug resistant virus, was not only extremely well tolerated, but was also potent and certainly superior compared to placebo + OBT. It was quite impressive to see an overall response of more than 90% for patients who were given raltegravir with enfuvirtide and/or TMC114.

The results presented from these four studies (MOTIVATE 1 and 2 and BENCHMRK 1 and 2) at this late breaker session were truly landmarks and have the potential to change treatment paradigms. Although we need to exercise caution given the relative preliminary nature of these data, it is difficult not to get too excited about the future possibilities for our treatment-experienced patients.

Gilead Sciences, Inc., is also developing an integrase inhibitor with different pharmacokinetic properties for use in experienced patients. The preliminary results of their phase 2b trial is also being presented at this conference. Two other companies, Schering-Plough Corporation and Incyte Corporation, have other CCR5 entry inhibitors that are currently in clinical development.

The availability of one of more of these integrase inhibitors and entry inhibitors, coupled with the recent availability of potent PIs such as tipranavir (TPV, Aptivus) and TMC114, and the use of enfuvirtide make treating the treatment-experienced patient much easier. With all these options, the use of a single-active drug, so-called sequential monotherapy, should be avoided since it usually leads to rapid development of resistance to that drug, further limiting future treatment options.

The benefits of plasma HIV-1 RNA suppression to less than 50 copies/mL on durability of response and the prevention of emergence of resistance support using persistent elevations above this cutoff as a definition of virologic failure. Previous treatment guidelines9 had recommended establishing a plasma HIV-1 RNA target of at least 0.5 to 1 log10 HIV-1 RNA copies/mL below baseline for patients with more advanced treatment failure and a high level of multidrug resistance. However, with all this data emerging from the evaluation of these new agents that are designed to have activity against multidrug-resistant virus, it is quite possible that a high proportion of our heavily treatment-experienced patients can now achieve HIV-1 RNA levels of less than 50 copies/mL. Thus the goal of therapy should always be the achievement of HIV RNA levels below 50 copies/mL, even for highly treatment-experienced patients.

This article was provided by TheBodyPRO.com. It is a part of the publication Exclusive Coverage of the 14th Conference on Retroviruses and Opportunistic Infections.

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